In general, ink jet printing machines or printers include at least one printhead that ejects drops or jets of liquid ink onto a recording or image forming media. A phase change ink jet printer employs phase change inks that are in the solid phase at ambient temperature, but transition to a liquid phase at an elevated temperature. The molten ink can then be ejected onto a printing media by a printhead directly onto an image receiving substrate, or indirectly onto an intermediate imaging member before the image is transferred to an image receiving substrate. Once the ejected ink is on the image receiving substrate, the ink droplets quickly solidify to form an image.
In both the direct and offset printing architecture, images may be formed on a media sheet or a media web. In a web printer, a continuous supply of media, typically provided in a media roll, is mounted onto rollers that are driven by motors. A loose end of the media web is passed through a print zone opposite the print head or heads of the printer. Beyond the print zone, the media is gripped and pulled by mechanical structures so a portion of the media continuously moves through the print zone. Tension bars or rollers may be placed in the feed path of the moving web to remove slack from the web so it remains taut without breaking.
In continuous-web direct to paper printing, a fixing assembly is typically used after the ink is jetted onto the web to fix the ink to the web. The fixing assembly used depends on the type of ink. For example, when using melted phase change ink to form images, the fixing assembly may include a spreader configured to apply pressure to the ink and media to spread the ink on the media. The function of the spreader is to transform a pattern of ink droplets deposited onto a media and spread them out to make a more uniform and continuous layer. The spreader uses pressure and/or heat to reduce the height of the ink droplets and fill the spaces between adjacent drops. In another example, when using an aqueous ink to form images, the fixing assembly may include a contact or non-contact heater used to reduce the water or other volatiles from the paper and ink and thereby, among other things, reduce any potential smear or damage from subsequent contact of the inked media surfaces.
Some direct marking, continuous web printers are configured to print images onto both sides of the web, also referred to as duplex printing. To enable duplex printing on a continuous web, a web transport system may be configured to guide a web through a first print station to print on the first side of the web, also referred to as the simplex side, then invert the web and either guide the web back through the first print station or guide the web through a print zone of a second print station for printing on the second side of the web, also referred to as the duplex side.
One difficulty associated with duplex printing in such systems is that when the media is passing through the print station for printing on the duplex side, the simplex side of the media is pressed against several surfaces and rollers, and may be exposed to different temperatures and pressures, such as the heat and/or pressure applied by the spreader. Such contact between the simplex side of the media and the surfaces of the printer as well as the temperatures and pressures associated with such surfaces may adversely impact the image quality of images formed on the simplex side of the media. One particular image quality defect that may result when printing on the duplex side of the media is a reduction of the glossiness of the images on the simplex side creating a simplex side versus duplex side gloss differential.